In the process of recording data onto a storage medium (such as magnetic tapes or bubbles and other similar data channels) and subsequently reproducing the data, the recorder/reproducer used, as well as the storage medium itself, may introduce errors. The most usual types of errors occurring in the playback of tape-recorded data result from impurities on or imperfections in the storage medium. The impurities may be dust, bits of oxide, or other extraneous particles on the storage medium which result in a momentary increase in the head-to-storage medium separation with a corresponding decrease in signal strength. The imperfections may be spots with a deficiency of oxide, excess backing, lumps of oxide, or bits of foreign matter incorporated in either the oxide or backing which result in either excessive head separation or a magnetic dead spot. The size of the affected area on the storage medium is generally of the order of or less than the spacing of the tracks, and hence it is usual for errors to occur in only one track at a time. However, the affected spot may cover many bits (hundreds or even thousands) in one track of a high-density digital recording system.
Previously employed methods have generally required the "backing up" and repositioning of the storage medium to the beginning of a record of data in order to detect errors and have required re-reading the record from the storage medium for error-correction. These requirements which are common in prior art systems, such as the well-known nine-track tape ASCII system, further require that there be gaps on the tape between successive records, a significantly negative feature where high-density packing is sought.
Some error-correction systems have been designed to correct burst errors, such as U.S. Pat. No. 3,478,313 and U.S. Pat. No. 3,859,630; however, they do not have the capabilities of continuously correcting a burst error of indeterminate length along a storage medium without the need for re-reading the record or leaving gaps.
Finally, no prior art apparatus or method discloses the positioning of parity bytes along a magnetic tape or such other storage medium track while encoding the data across the tracks of such storage medium.